Temporal correlation between ecdysteroids and mitotic activity in larval tissues of Clitumnus extradentatus (Phasmoptera : Phasmatidae : Lonchodinae)

A comparative study of mitotic activities and haemolymph ecdysteroid levels was performed in the phasmid Clitumnus extradentatus. Temporal correlation was found between increases in mitotic frequency in mandibular and general epidermis, and variations of ecdysteroid levels in the haemolymph of the i nsects. Whereas, mitotic waves occurring in the fat body cells or in the ba sal cells of the midgut did not appear to be strictly correlated with these hormonal variations. During the fourth larval instar of this phasma; an ac curate study of mitotic figures, monitored from histological sections, indi cated a time-lag in their stimulation according to the studied area, with a peak on day 2 in the mandible tips, on day 5 in the mandible bases and on day 7 in the head capsule, thorax and abdomen epidermis: namely a five-day delay with respect to the 12 days of the fourth instar. Simultaneously, the evolution of ecdysteroid levels in the haemolymph showed three increases o f different importance. Each hormonal increase occurred 24 h before the tri ggering of each increase in the mitotic activity, whereas a fourth and very high peak, occurring on day 8, corresponded to the sudden fall in the numb er of epidermal mitoses.